U.S. patent number 4,897,591 [Application Number 07/047,413] was granted by the patent office on 1990-01-30 for regulated battery charger.
This patent grant is currently assigned to Fisher Scientific Group Inc.. Invention is credited to Wayne M. Spani.
United States Patent |
4,897,591 |
Spani |
January 30, 1990 |
Regulated battery charger
Abstract
The present invention is an electrical circuit for regulating
the average current through and the voltage across a load, such as
a rechargeable battery. The circuit includes at least one
semiconductor switching device connected in series with the load
for controlling the current through the load. A current control
loop is provided in the circuit to maintain the average current
through the load at a constant level despite changes in the
resistance of the load. Also provided is a voltage control loop
which acts to limit the voltage across the load to a value below a
predetermined voltage level.
Inventors: |
Spani; Wayne M. (San Diego,
CA) |
Assignee: |
Fisher Scientific Group Inc.
(San Diego, CA)
|
Family
ID: |
21948830 |
Appl.
No.: |
07/047,413 |
Filed: |
May 6, 1987 |
Current U.S.
Class: |
320/164 |
Current CPC
Class: |
H02J
7/0072 (20130101); H02J 7/007182 (20200101); H02M
3/156 (20130101); H02J 7/00711 (20200101) |
Current International
Class: |
H02M
3/04 (20060101); H02J 7/00 (20060101); H02M
3/156 (20060101); H02J 007/04 () |
Field of
Search: |
;320/20,21,22-24,31,32,39,40 ;323/319 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Sensitive Gates SCRS--Don't forget the Gate-Cathode Resistor" by
T. Malarky in Engineering Bulletin. .
"Charger Circuits" by Barcus et al. in Gates Battery Charger
Application Manual, 1982. .
"Guide to Thyristor Applications" in Motorola Semiconductor
Products, Inc., 1982. .
"SCR and Triac Power Control Fundamentals" in Motorola
Semiconductor Products Inc., 1978. .
"Charging" in Yuasa Battery Co., Ltd. Application Manual, 1986.
.
"General Characteristics" in Panasonic Sealed Lead-Acid Batteries
Technical Handbook, 1985. .
"Battery Charging Regulator" by Connolly et al. in General Electric
SCR Manual Sixth Edition, 1979..
|
Primary Examiner: Hickey; R. J.
Attorney, Agent or Firm: Nydegger & Harshman
Claims
What is claimed and desired to be secured by U.S. Letters Patent
is:
1. A circuit for regulating the average current through and the
voltage applied across the first and second terminals of a load,
the circuit comprising:
a transformer secondary having two end terminals and a center tap,
the center tap being connected to the first terminal of the
load;
a pair of individually and selectively operable switching elements,
each of said switching elements being connected between the second
terminal of the load and a respective one of the end terminals of
the transformer secondary, each of said switching elements during
the duty cycle thereof completing a closed current path in which
current flows through the load in a single common current flow
direction;
a sense element comprising a resistance of less than 1 ohm
connected in series with the load for producing a sensed voltage
proportional to the current through the load;
a current control loop connected to the sense element and the
switching device, the current control loop adapted for controlling
the duty cycle of the switching elements to maintain a constant
average current through the load;
means for establishing a preselected threshold voltage; and
a voltage control loop having a comparator circuit for comparing
the voltage present at the terminals of the load and a preselected
threshold voltage for flexibly decreasing the duty cycle of the
switching elements controlled by the current control loop, to
maintain charging current above a trickle charge in proportion to
the amount by which said load voltage exceeds said threshold
voltage, and maintaining said load voltage at or below said
preselected threshold voltage.
2. A circuit as defined in claim 1 wherein the load comprises a
battery.
3. A circuit as defined in claim 1 wherein the switching elements
comprise semiconductor switching devices.
4. A circuit as defined in claim 3 wherein the semiconductor
switching elements comprise silicon controlled rectifiers.
5. A circuit as defined in claim 4 wherein the current control loop
comprises:
integration means for integrating the sensed voltage produced by
the sensing element and for producing therefrom an integrated
signal representing the average current flow through the load;
and
comparison means for comparing the integrated signal to a reference
voltage and producing a corresponding control signal.
6. A circuit as defined in claim 5 wherein the integration means
comprises an amplifier configured as an integrator.
7. A circuit as defined in claim 6 wherein the amplifier has a gain
greater than one.
8. A circuit as defined in claim 6 wherein the integration means
further comprises an RC circuit connected to the output of the
amplifier.
9. A circuit as defined in claim 5 wherein the comparison means
comprises a comparator and a reference voltage generator.
10. A circuit as defined in claim 5 wherein the comparison means
comprises a first and a second inverting comparator, the output of
the first comparator being connected to the inverting input of the
second comparator.
11. A circuit as defined in claim 10 the current control loop
further comprises isolation means for isolating the output of the
second comparator from the switching device.
12. A circuit as defined in claim 11 wherein the isolation means
comprises an opto-isolator.
13. A battery charging circuit comprising:
an alternating current power source comprising a secondary winding
of a transformer, the secondary winding having first and second end
terminals and a center tap, the center tap being connected to a
first terminal of the battery;
a switching device connected in series with the battery for
permitting current flow in a single direction therethrough, the
switching device comprising first and second semiconductor
switching elements each having a first and a second current
carrying terminal, the first current carrying terminal of each
semiconductor switching element being connected to a second
terminal of the battery, the second current carrying terminal of
the first semiconductor switching element being connected to the
first end terminal of the secondary winding, and the second current
carrying terminal of the second semiconductor switching being
connected to the second end terminal of the secondary winding;
sensing means connected in series with the battery and the
switching device for producing a sensed voltage proportional to the
current through the battery;
averaging means for averaging the sensed voltage to produce an
averaged sensed voltage;
comparison means comprising an opto-isolator connected between the
comparator and the switching device, the opto-isolator responding
to the control signal to control the duty cycle of the switching
device for comparing the averaged sensed voltage to a reference
voltage and for controlling the duty cycle of the switching
elements to maintain a preselected constant charge current through
the battery if the averaged sensed voltage deviates from a value
corresponding to the preselected current; and
overvoltage protection means comprising a voltage comparator
circuit having at least one input and an output, the voltage across
the battery terminals being applied to one input of the voltage
comparator circuit and the output of the voltage comparator being
connected to the comparison means to flexibly decrease the duty
cycle of the switching elements controlled by the comparison means
to flexibly decrease the charging current when battery voltage
equals or exceeds said predetermined threshold voltage, in
proportion to said voltage excess.
14. A circuit as defined in claim 13 wherein the switching elements
comprise silicone controlled rectifiers.
15. A circuit as defined in claim 13 wherein the sensing means
comprises a resistive element connected in series between the
battery and the switching device.
16. A circuit as defined in claim 13 wherein the averaging means
comprises an amplifier.
17. A circuit as defined in claim 16 wherein the averaging means
further comprises an RC circuit connected to the output of the
amplifier.
18. A circuit as defined in claim 13 wherein the comparison means
comprises a comparator configured to compare the averaged sensed
voltage to a first reference voltage and to produce a corresponding
control signal.
19. A circuit for maintaining a constant average charge current
through a rechargeable battery and for preventing overcharging of
the battery, the circuit comprising:
(a) a switching device connected in series with the battery for
permitting current flow in a single direction therethrough, the
switching device comprising first and second semiconductor
switching elements each having first and second current carrying
terminals, the semiconductor switching elements being connected
parallel one to another at one terminal of the battery by said
first current carrying terminals;
(b) a sensing element adapted for producing a sensed voltage
proportional to the charge current;
(c) a current control loop comprising:
(i) averaging means comprising an amplifier, and further comprising
an RC circuit connected to the output of said amplifier for
averaging the sensed voltage to produce at an output thereof an
average sensed voltage;
(ii) comparison means for comparing the average sensed voltage to a
reference voltage to produce a corresponding control signal;
(iii) isolation means comprising an opto-isolator, the output of
the opto-isolator being connected to the switching device and being
responsive to the control signal for controlling the switching
device to maintain through the battery a constant charge current;
and
(d) an overvoltage protection loop comprising:
(i) means for comparing the voltage across the battery terminals to
a reference voltage; and
(ii) means for flexibly reducing the charge current to a level
equal to or greater than a trickle charge when the voltage across
the battery terminals reaches a predetermined threshold voltage,
and maintaining said battery terminal voltage at a level equal to
or below said predetermined threshold voltage.
20. A circuit as defined in claim 19 wherein the first and second
semiconductor switching elements comprise silicon controlled
rectifiers.
21. A circuit as defined in claim 19 further comprising a
transformer secondary winding having first and second end terminals
and a center tap, the center tap being connected to one terminal of
the battery, the first end terminal of the transformer secondary
being connected to the first end terminal of the first switching
element and the second end terminal of the transformer secondary
being connected to the first end terminal of the second switching
element.
22. A circuit as defined in claim 19 wherein the means for reducing
the charge current is connected to the output of the averaging
means.
23. A circuit for charging a battery from an AC power line, the
battery having first and second terminals and the circuit
comprising:
a transformer having a secondary winding provided with first and
second end terminals and a center tap, the center tap being
connected to the first terminal of the battery;
a resistive element having first and second terminals, the first
terminal of the relative element being connected to the second
terminal of the battery;
two semiconductor switching devices for permitting current flow in
a single direction through the battery, each of the semiconductor
switching devices having first and second current carrying
terminals and a control terminal, the first current carrying
terminal of each of the switching devices being connected to the
second terminal of the resistive element, the second current
carrying terminal of the first semiconductor switching device being
connected to the first end terminal of the secondary winding, and
the second current carrying terminal of the second semiconductor
switching device being connected to the second end terminal of the
secondary winding;
averaging means for averaging the voltage across the resistive
element to produce as an output an averaged sensed voltage;
means for producing a reference voltage;
comparison means comprising an opto-isolator connected between the
comparator and the switching device, the opto-isolator responding
to the control signal to control the duty cycle of the switching
device for comparing the averaged sensed voltage to the reference
voltage and for producing a corresponding control signal, the
control signal being applied to the control terminals of the
semiconductor switching devices to control the duty cycle of the
semiconductor switching devices and maintain the current through
the battery at a constant level; and
overvoltage protection means comprising a voltage comparator
circuit having at least one input and an output, the voltage across
the battery terminals being applied to one input of the voltage
comparator circuit and the output of the voltage comparator being
connected to the comparison means to monitor the voltage across the
terminals of the battery and to maintain the voltage across the
terminals of the battery at a level equal to or less than a
predetermined threshold voltage by modifying comparison means
control of the duty cycle of the semiconductor switching devices to
flexibly reduce the duty cycles thereof, according to the
relationship between said battery voltage equal and said threshold
voltage.
Description
BACKGROUND
1. The Field of the Invention
The field of the present invention generally relates to regulated
electrical power supplies. More specifically, the present invention
relates to electrical circuits for providing constant current
regulation as well as overvoltage limitation and which are
particularly well adapted for use as a battery charger.
2. The Background Art
Nearly all modern electronic devices require what is generally
termed a "power supply" in order to conveniently operate the device
from available sources of electricity. The most common of these is
the AC power line. It is the function of a power supply to convert
the alternating current found on the power line, which is often at
potentials which range between 100 and 240 volts rms, to a
rectified voltage generally in the range from 6 to 24 volts. Thus,
the functions of a power supply are the transformation of the high
power line voltages to a lower voltage and rectification of the
current flow. It is often the case that a conventional power supply
is used to charge what are referred to as a secondary cell, i.e., a
rechargeable battery.
Generally, a power supply contains a transformer and a rectifier
circuit. Additionally, a capacitor, as well as other components,
may also be used in order to provide filtering to reduce the ripple
present in the output voltage. While such a simple power supply may
properly power some electronic circuits and devices, for optimum
performance it is often necessary that the power supply be
regulated. This is also true for secondary electrochemical
cells.
The term "regulated" refers to the characteristic of a power supply
whereby under varying load conditions (e.g., varying resistance)
either the voltage or the current through the load will remain
constant. Voltage regulation or current regulation is provided by
an electrical circuit which is incorporated into the power supply
in addition to the transformer, rectifiers, and any additional
filtering components. It is nearly always the case that any
electrical circuit acting as a load will perform more reliably and
consistently if power is provided to it by a regulated power
supply. The use of regulated power supplies also allows maximum
performance from secondary electrochemical cells, groups of which
are referred to as batteries. Since a battery charger is merely a
specialized form of a power supply, the two terms will be used
interchangeably throughout this disclosure.
The term "secondary cell" generally refers to an electrochemical
cell which produces a voltage across its terminals and is capable
of being recharged to its original state after being discharged.
The operation of a secondary cell is in contrast to that of a
primary cell, which must be discarded after it becomes discharged.
It is uncommon, however, to use a single secondary cell. Rather, a
plurality of secondary cells are connected in series to form a
battery. For convenience, rather than referring to a secondary
cell, the terms "rechargeable battery" or just "battery" will be
used herein. Use of the term "battery" is intended to encompass
both single secondary cells and rechargeable batteries.
Regulated power supplies and regulated battery chargers may be
designed to have several different attributes. The most common of
these are constant voltage and constant current. The constant
voltage regulated power supply is designed to provide a constant
voltage, regardless of the amount of current that is drawn or
"sinked," by the load, which in the case of a charger is a battery.
Alternatively, a constant current regulated power supply is
designed to provide a constant current regardless of the voltage
required in order to maintain the constant current flow. It will be
appreciated that the actual performance of regulated power supplies
are far from the ideal.
For example, it is often impractical to design and construct a
constant voltage power supply which is capable of delivering
"unlimited" current. Similarly, it is impractical, as well as
impossible in some cases, to design and construct a constant
current regulated power supply which will maintain a constant
current through any load. Furthermore, some power supplies are
designed to operate as a constant current supplies under some
conditions and constant voltage supplies under others.
It is the application that substantially determines the type of
regulation desired. A transistorized amplifier generally requires a
constant voltage in order to operate properly. Alternatively, the
charging of batteries is best carried out with a constant current.
Rechargeable batteries are finding expanded applications in many
industrial, scientific, medical, and consumer situations. Thus,
providing efficient chargers is becoming more important as more
applications for rechargeable batteries are found.
One of the most common examples of a rechargeable battery is the
lead-acid battery used to power the starter in nearly all
automobiles. A particular variant of this class of batteries is the
so-called "gel-cell" battery in which the electrolyte is a highly
viscous gel and the case is sealed. Since the lead-acid battery is
impractical in many circumstances, other types of rechargeable
batteries have been developed, including what are commonly referred
to as nickel cadmium batteries. Modern nickel cadmium batteries
have a useful lifetime extending through hundreds, or even
thousands, of charge-and-discharge cycles. The popularity of nickel
cadmium, or Ni-Cad, batteries is increasing, as they find more and
more applications in many different fields.
As stated earlier, a constant current power supply is most useful
for recharging batteries. This will be appreciated by understanding
that the rechargeable battery is an electrochemical device. The
rate of electrochemical reaction, assuming constant temperature, s
generally current dependent. Thus, the material liberated in
discharging an electrochemical cell (e.g., rechargeable battery) is
directly proportional to the quantity of current circulated through
the cell. In other words, for each ampere of current supplied by
the cell during the discharge process, a calculable mass of
material is liberated. This electrochemical reaction is reversed
during the recharging process. For each ampere of current
circulated through a cell in an ideal rechargeable battery, a
certain mass of material will be deposited, until all of the
material liberated during the discharge process has been recombined
and the rechargeable battery is fully charged.
Importantly, the voltage found across the terminals of a battery is
not an accurate indication of the state of charge of the battery.
Interestingly, one of the desirable properties of "gel-cell" as
well as Ni-Cad batteries is that the terminal voltage remains
constant until the capacity of the battery is nearly exhausted. The
same is true during the recharging process. The terminal voltage
rapidly rises to a nominal voltage even through the battery may
have only been recharged to ten percent of capacity.
Thus, monitoring the voltage found at the battery terminals is not
an accurate indication of the state of charge of the battery. An
excessively high terminal voltage, however, is indicative of an
"overcharged" condition. Furthermore, the internal resistance of
the battery to the "charging current" will vary greatly during the
recharge process, generally being lowest when the battery is
completely discharged and highest when the battery has reached its
maximum charge.
Thus, if it is desired to recharge a battery within for example,
four hours, the application of a constant voltage will not assure
that full recharge takes place within the desired time. This is due
to the fact that the internal resistance of the cell varies during
recharging, and the amount of current passing through the battery
will also vary. The application of whatever voltage is necessary to
maintain a constant current, will on the other hand allow the
battery to be predictably fully recharged within a desired time.
Thus, in order to reliably recharge a battery within a desired
amount of time, a battery charger should be regulated to provide a
constant current.
There exist two principal methods of implementing power supply
regulation: dissipative regulation and switching regulation.
In dissipative-type regulators, an electronic device, such as a
transistor or vacuum tube, is operated linearly to control the flow
of current through it, and thus also the voltage drop across it.
Modern power supplies generally use transistors. The transistor may
be configured in a series pass arrangement (where all the current
flowing to the load passes through the transistor) or a shunt
arrangement (where the current is shunted through the transistor
rather than being allowed to flow through the load). The linear
operation of the transistor allows very accurate regulation since
the current or voltage supply to the load may be varied in very
small increments.
It is important to note that the dissipative-type regulators
inherently operate at low efficiencies. The following example will
illustrate the low efficiency of the dissipative-type regulators.
Assume that a "series pass" transistor is controlling the current
to the load at a constant level. Also assume that a constant
current of one ampere is flowing through the series pass transistor
and the load and that the voltage drop across the load is 35 volts.
If there is a voltage drop of two volts across the series pass
transistor, the transistor would be required to dissipate a mere
two watts of power and heat.
If on the other hand, the voltage required to maintain a current of
one ampere diminishes to 20 volts, in order to maintain the current
at a constant one ampere, the series pass transistor would be
required to experience a drop of 17 volts. Thus the transistor
should be capable of dissipating 17 watts of power and heat. The
seriousness of this situation is dramatic where it is known that
wide variations in voltage will be experienced while constant
current is to be maintained.
In situations where wide voltage swings will be experienced, such
as when charging batteries, it is necessary to set the operating
point of the series pass transistor at approximately the middle of
the expected voltage range. Thus, dissipative-type regulators
inherently operate at efficiencies of 50% to a maximum 60% and are
particularly inefficient when operating at the extremes of the
voltage ranges, depending upon the particular type of circuit used
in the regulator.
While the efficiency of electronic circuits is always a concern to
the circuit designer and builder, in many applications the power or
heat dissipated by a regulator is of greater concern. For example,
in the medical arts, it is common to incorporate rechargeable
batteries in medical devices, such as infusion pumps. Inclusion of
rechargeable batteries in medical devices allows the devices to
continue to provide life support functions even when AC power is
removed. The use of rechargeable batteries and built-in rechargers
allows the battery to be maintained in a fully charged condition
and thus to be available for use at any time without the need for
constant operator surveillance.
Dissipative-type regulators have a serious drawback in such
applications. It is generally desirable to make such medical
devices as small as possible. Furthermore, it is also desirable to
enclose such devices in sealed housings without any
ventilation.
As is well known, increases in component temperature cause dramatic
increases in the failure rates of those components. For example, it
has been found that for every 10.degree. centigrade rise in
temperature, components commonly found in medical devices
experience a twofold increase in their failure rates. This effect
of heat generated by dissipative-type regulators is an especially
serious consequence in medical devices where component failure can
be potentially life threatening.
In contrast to the operation of dissipative-type regulators are the
switching-type regulators. In switching-type regulators the
linearly operating series pass element found in dissipative-type
regulators is replaced by a switching device. Such switching
devices should have the characteristics of an ideal switch, that
is, infinite resistance when turned off and zero resistance when
closed, or turned on. Modern transistors provide very good
approximations of these ideal characteristics. When used as
constant current regulators, the amount of time that the switching
device is on constitutes its duty cycle and determines the average
current through the load.
Since switching devices, such as transistors, SCRs, triacs, or
similar devices, are either on or off, very little power loss is
experienced. According to Ohm's law, power generated equals I.sup.2
R. When the switch is conducting and the resistance is zero; when
it is not conducting the current is zero. Thus power dissipation
will in theory be zero. While switching-type regulators often
require more components than their dissipative-type counterparts,
it is still possible to realize considerable savings in volume and
weight with them, since much smaller and lighter weight components
can be used. In particular, large filter capacitors are not
needed.
Thus, the inherently higher efficiency, and lower heat generation,
as well as the savings in volume and weight, make switching-type
regulators compatible for use in medical device applications, such
as described above. Switching-type regulators, however, inherently
have other drawbacks.
First, switching-type regulators have much less precise regulation
than their dissipative-type counterparts. In order to increase the
precision of the regulation, it is necessary to increase the
switching rate. Increasing the switching rate, however, leads to a
second drawback. As the switching rate is increased to improve
regulation precision, switching transients are produced a very high
and higher frequencies. Thus, even reasonably precise
switching-type regulators can produce an excessive amount of radio
frequency interference. Unless deliberate precautions are taken to
reduce the radiation of radio frequency interference, severe
interference with the operation of surrounding devices can
occur.
By an understanding of the foregoing, it will be appreciated that
it would be an advance in the art to provide a regulated battery
charger which maintains a high efficiency over a widely varying
range of voltages. It would also be an advance in the art to
provide a battery charger which generates very little heat and thus
is suitable for use in enclosures lacking ventilation. Still
further, it would be an advance in the art to provide a regulated
battery charger with the above attributes which requires relatively
few components and which when assembled occupies a very small
volume of space.
It would be yet another advance in the art to provide a regulated
battery charger which combines the above advantages and which
radiates an inconsequential amount of radio frequency interference.
Another advance in the art would be to provide a regulated power
supply incorporating all of the above listed attributes which
exhibits regulation precise enough and current carrying capacities
high enough to suit it for use as a battery charger.
These and other advantages provided by the present invention over
the devices found in the art will become more fully apparent with
an understanding of the present invention gained by an examination
of the following description of the preferred embodiment.
BRIEF SUMMARY AND OBJECTS OF THE INVENTION
The present invention is an electrical circuit for regulating the
average current through, and the voltage across, a load. The
invention has particular use when the load is a rechargeable
battery. The circuit of the present invention comprises at least
one switching device connected in series with the load. In the
preferred embodiment of the present invention, two semiconductor
switching devices are used in cooperation with a transformer having
a secondary provided with first and second end terminals and a
center tap. Each end terminal of the secondary is connected to a
first current carrying terminal of each semiconductor switching
device, while the center tap is connected to a first terminal of
the load.
A current control loop is provided to maintain the current through
the load at a constant value. Part of the current control loop is a
sensing element interposed between a second terminal of the load
and the second current carrying terminals of the semiconductor
switching devices. As current flows through the sense element a
sensed voltage is generated representative of the current flowing
through the load. The remainder of the current control loop
averages the sensed voltage, compares it to a first reference
voltage, and produces a control signal which controls the duty
cycle of the semiconductor switch devices to accurately maintain
the average current through the load at a constant level.
The present invention is also provided with a voltage control loop
or overvoltage protection circuit. The voltage control loop
monitors the voltage across the terminals of the load, compares
this voltage to a second reference voltage, and interrupts the
current control loop so that the current through the load will
decrease or even terminate, if the voltage across the terminals of
the load exceeds a predetermined threshold voltage.
It will be appreciated that a primary advantage of the present
invention is that it is much more efficient than dissipative-type
regulators or chargers, which operate at about a 50% to 60%
efficiency. While ordinary switching-type regulators operate at
about 70% to 75% efficiency, most generate excessive radiofrequency
interference (RFI) which requires the addition of shielding in
order to comply with Federal Communications Commission rules. The
addition of shielding, or other components to reduce RFI, adds both
bulk and weight to the charger or regulator, both of which need to
be kept at a minimum in medical devices such as infusion pumps.
While the present invention operates at efficiencies of about 66%
to 77%, it does not generate significant amounts of RFI and thus
does not have the disadvantages normally associated with
conventional switching-type regulators.
In view of the foregoing, it is a primary object of the present
invention to provide a regulated battery charging circuit which
exhibits high efficiency over a wide range of voltages.
Another object of the present invention is to provide a charger or
regulator which occupies a minimum amount of space.
Yet another object of the present invention is to provide a power
regulation or battery charging circuit which generates little heat
and thus is suitable for use in compact and unventilated
enclosures.
Still another object of the present invention is to provide a high
efficiency, compact regulated battery charging circuit which does
not radiate consequential amounts of radio frequency
interference.
Yet another object of the present invention is to provide a battery
charger circuit which monitors the terminal voltage of the battery
and limits the current flowing through the battery in order to
prevent overcharging.
Still another object of the present invention is to obtain a
battery charger circuit which is compact and efficient, and which
provides a constant charge current through a battery.
These and other objects of the present invention will become more
fully apparent after consideration of the following description
provided herein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 diagram illustrating the major functional blocks of the
present invention.
FIG. 2 is schematic diagram showing the major components used in
one embodiment of the present invention, wherein the boxes in
dashed lines correspond to functional blocks illustrated in FIG. 1
to indicate which components perform each function.
FIG. 3 a detailed schematic diagram showing the precise
configuration of the components used in a presently preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will now be made to the drawings to explain the structure
and operation of a presently preferred embodiment of the invention.
Reference will first be made to FIG. 1 for a general overview of
the structure and function of the present invention and then to the
simplified schematic of a preferred embodiment illustrated in FIG.
2. It should be appreciated that the embodiments depicted in the
figures are merely intended to be illustrative. It is specifically
contemplated that the present invention may take many different
forms and be used in many different applications other than merely
those illustrated herein.
1. General Structure and Function of the Present Invention
The major functional blocks of a circuit 100 according to the
present invention are illustrated in FIG. 1. Block 102 labeled "AC
Power" represents a source of alternating current which is of
sufficient current supplying capacity to satisfy the needs of the
load. The load in FIG. 1 is represented by block 114 labeled
"Battery." It should be appreciated that loads other than battery
cells could be used with the present invention, however, the
present invention is most particularly adapted for efficient
charging of batteries.
Block 106 labeled "Switching Device" represents an electrical
device capable of acting as a switch. While it is presently
contemplated that a semiconductor switch device will be used, such
as a transistor, silicon controlled rectifier (SCR), or triac, it
is possible that mechanical or vacuum tube type devices could also
be used. Mechanical or tube type devices generally would, however,
cause a decrease in performance in most applications.
The two most important features of the Switching Device are first
that the device should exhibit characteristics as close as possible
to an ideal switch by possessing infinite open-circuit impedance
and zero closed-circuit impedance, and second that the device
should be able to change states extremely quickly, at least on the
order of microseconds. The switching device must also have
sufficient current carrying capacity. It will be appreciated that
generally only semiconductor switching devices are capable of
fulfilling these requirements. Devices may, however, be fabricated
in the future which fulfill these requirements and which are more
desirable than the semiconductor switching devices mentioned above.
These are contemplated as within the scope of the switching devices
appropriate for use in the present invention.
As can be seen in FIG. 1, Switching Device 106 is connected in
series between AC Power 102 and Battery 114 by lines 104 and 108.
Line 132 connected between Battery 114 and AC Power 102 represents
the completion of the closed current path from AC Power 102 through
Switching Device 106 and Battery 114 back to AC Power 102 Thus it
will be appreciated that all the current flowing through Battery
114 also flows through Switching Device 106 and Switching Device
106 is able to control the flow of current through Battery 114.
When used as a battery charger, the present invention is best
principally configured as a constant current supply. That is, it is
generally desirable to maintain the charge current through Battery
114 at a constant level so that charging can be predictably
controlled. The current through line 108 is monitored and expressed
as a voltage by block 110 labeled "Sensing Element." Sensing
Element 110 should be constructed so as to only minimally affect
the current flow through line 108, but still to provide an accurate
indication of the current flow. Thus, line 108 is broken as it
passes through block 110 to indicate that Sensing Element 110
monitors the current through line 108 but does not substantially
affect it.
The voltage expressed by Sensing Element 110 is conveyed to block
124, labeled "Current Sensing Loop." Current Sensing Loop 124
produces a signal, which is represented by arrow 126, to control
the duty cycle of Switching Device 106 to maintain the average
current through Battery 114 at a constant level.
Since Switching Device 106 is controlling a flow of current from AC
Power 102 that is alternating, average current through Battery 114
is controllable by changing the state of Switching Device 106 at
various times in the AC power cycle. Thus, if a greater amount of
average current is required, the length of time Switching Device
106 is closed will be increased, lengthening the duty cycle
thereof. Average current in this context is understood to be the
total charge that flows through Battery 114 during a given number
of cycles of the AC power cycle averaged over the period of time
corresponding to that number of cycles.
It is important that Battery 114 not be overcharged. Thus, the
present invention includes an overvoltage protection circuit,
represented by block 118 and labeled "Voltage Sensing Loop."
Voltage Sensing Loop 118, which is interfaced to Current Sensing
Loop 124 by line 120, monitors the terminal voltage of Battery 114.
When the terminal voltage of Battery 114 reaches a predetermined
threshold voltage, Voltage Sensing Loop 118 interrupts the
operation of Current Sensing Loop 124 with a control signal
represented by arrow 120. This prevents the voltage across the
terminals of Battery 114 from increasing further and permits it to
decrease to a safe level.
Block 130 labeled "DC Power" represents a DC power source which
supplies the current and voltage required to operate the active
components of Voltage Sensing Loop 118 and Current Sensing Loop
124. DC power is connected to Voltage Sensing Loop 118 and Current
Sensing Loop 124 by a
2. Description of the Structure of the Preferred Embodiment
Reference will be now be made to FIG. 2, which is a simplified
schematic diagram of one embodiment of a circuit 200 embodying the
present invention.
It should be appreciated that many different components and
arrangement of those components, could be devised to carry out the
invention by those skilled in the art. Also, as illustrated in FIG.
3, additional components may be necessary to best implement the
invention. The simplified schematic diagram illustrated in FIG. 2,
however, is deemed best suited to providing an understanding of the
structure and operation of the major components of the invention.
As a matter of convention, in FIGS. 2 and 3, when two lines meet no
connection is intended unless a dot is provided at their
intersection. Further, for purposes of clarity, in FIG. 2 the
current paths through circuit 200 that carry a "high" current of
between two and twenty amperes are shown by bold lines.
In FIG. 2, all of the major functional blocks illustrated in FIG. 1
have also been included in the form of boxes in dashed lines which
have been labeled with the same reference numerals as used in FIG.
1 for corresponding functional blocks. For example, the components
carrying out the functions represented by block 102 labeled "AC
Power" in FIG. 1 are contained within box 102 of FIG. 2.
The components performing the function of Switching Device 106 in
FIG. 1, are included within box 106 of FIG. 2. These include
silicon controlled rectifiers 220 and 224 (SCRs). The remaining
components in block 106 are associated with SCRs 220 and 224 are
necessary for SCRs 220 and 224 to operate properly. Bearing in mind
that efficiency is an object of the present invention and that two
SCRs perform more efficiently than one, the switching function may
alternatively be carried out by a single discrete device.
The Battery 114 in FIG. 1 is represented by battery 234 contained
within box 114 of FIG. 2. "Gel-cell" batteries are generally
preferred as the rechargeable battery for use with the present
invention, however, many other types of rechargeable batteries
presently known, or devised in the future, may be used with the
present invention.
Box 110 of FIG. 2 corresponds to Sensing Element 110 of FIG. 1 and
includes a resistor 232. Resistor 232 is but one of the devices
that can be used as the Sensing Element represented by Block 110
shown in FIG. 1. In the embodiment illustrated in FIG. 2, resistor
232 is connected between battery 234 and SCRs 220 and 224 and has
been chosen to produce a voltage proportional to the current
through battery 234 without substantially affecting that current
flow. It will be appreciated, however, that other structures and
methods could be used to measure the current through battery 234.
For example, a sensing loop encircling a terminal of battery 234
would result in an induced voltage proportional to the current
through battery 234 and might also be used for the same
purpose.
The components performing the function of Current Sensing Loop 124
in FIG. 1, are contained within box 124 in FIG. 2. Likewise, the
function of Voltage Sensing Loop 118 in FIG. 1 is performed by the
box 118 in FIG. 2. Voltage Sensing Loop 118 will also be referred
to herein as an overvoltage protection circuit.
The components within box 130 in FIG. 2 carry out the functions of
DC Power 130 in FIG. 1. The purpose of components contained in box
130 is to provide DC power for the active components contained in
the other functional blocks of circuit 200.
Having explained the overall arrangement of major functional blocks
of the preferred embodiment, the individual components of each
functional block will now be identified and described. It should be
appreciated that the specific components described, and their
particular values, are merely representative of the components and
values which those skilled in the art will appreciate could be used
to carry out the present invention.
Within box 102 is a transformer having a laminated iron core 210
and a primary winding 208 connected to an AC power source 202 by
way of transformer primary terminals 204 and 206. Circuit 200 in
FIG. 2 is intended to be powered by an AC power source 202
operating in an anticipated frequency range of between 50 and 60 Hz
at a level of 120 volts rms. The circuitry disclosed, however, is
capable of functioning satisfactorily at any line frequency in the
range of 25 to 400 Hz. It will also be appreciated that AC power
source 202 must be able to supply sufficient current for proper
operation of circuit 200. This generally would not be deemed a
problem, however, as circuit 200 is intended to require less than
20 amperes. A transformer secondary, generally indicated at 212, is
provided with first and second terminals 214 and 218, respectively,
as well as a center tap 216. Secondary 212 is configured to provide
8 volts between center tap 216 and each of secondary end terminals
214 and 218.
Center tap line 216 is connected to a first terminal 234A of
battery 234. A second terminal 234B of battery 234 is connected to
a first terminal 232A of resistor 232. As explained earlier, the
purpose of resistor 232 is to create a voltage which is directly
proportional to the current through battery 234. The resistance of
resistor 232 is generally very low and may be 0.033 ohm. Thus, it
is preferred that resistor 232 be capable of dissipating at least
0.2 watt of power in order to allow the average current of 2.5
amperes to flow through battery 234. Second terminal 234B of
battery 234 and first terminal 232A of resistor 232 are connected
to the circuit common 300.
A second terminal 232B of resistor 232 is connected to SCRs 220 and
224 at the anodes 220A and 220B thereof, respectively. SCRs 220 and
224 each include in addition cathodes 220B and 224B, respectively,
and gates 220C and 224C, respectively. For convenience, the anode
or cathode of a device, such as an SCR, will when appropriate be
referred to hereafter using the term "current carrying terminal."
This will distinguish such terminals from the gate or other control
terminal of the device. SCRs 220 and 224 are identical and may be
of the type generally designated in the art as S4060F.
It is important that SCRs 220 and 224 have sufficient current
carrying capacity, an adequate peak inverse voltage rating, and the
lowest possible forward biased resistance so that power dissipated
by SCRs 220 and 224 will be minimized.
SCRs 220 and 224 are each provided with the associated components
shown within box 106. Resistor 222 is necessary to properly bias
SCR 220. Resistor 222 is connected between gate 220C and cathode
220B of SCR 220. Resistor 222 has a value of approximately 1 Kohms.
Cathode 228B of diode 228 is connected to the gate 220C of SCR 220.
Diode 228 is a silicon diode of the type generally known in the art
as lN4148. Similarly, SCR 224 has associated with it resistor 226
and diode 230 which function in a similar fashion and preferably
are identical to resistor 222 and diode 228, respectively. Cathode
220B of SCR 220 is connected to first transformer secondary end
terminal 214. Cathode 224B of SCR 224 is connected to second
transformer secondary end terminal 212. Thus, a closed current path
is provided from center tap 216 through battery 234, resistor 232,
and SCR 220 to first transformer secondary terminal 214. Similarly,
a closed current path is provided from center tap 216 through
battery 234, resistor 232, and SCR 224 to second transformer
secondary terminal 214. Thus, a current loop is provided through
battery 234 which may be readily controlled by SCRs 220 and
224.
The current through a battery during the recharge procedure is
generally referred to as the "charge current." A charge current may
be either direct current or pulsed direct current, since it is
principally the total number of electrons flowing through the
battery that is of concern during charging, regardless of whether
the instantaneous current is constant. Nevertheless, it is very
desirable that the average charge current be maintained constant so
that the charging status may be more reliably predicted.
If a charge current is too high, it may lead to excessive heat
within the battery, thus causing destruction or damage to the
battery or other nearby components. Alternatively, a charge current
which is too low will not charge the battery within the desired
time period. In the embodiment illustrated in FIG. 2, it is
contemplated that a 6-volt "gel-cell" battery rated at 10 amp
hours, such as battery model LCR-1006P manufactured by Panasonic
will be used.
The circuit 200 illustrated in FIG. 2 is configured so that the
average charge current will be maintained at approximately 2.3
amperes. Using a 6 volt, 10 amp hour battery, a charge current of
2.3 amperes will fully charge the battery within four hours without
generating excessive heat. The normal terminal voltage of such a
battery when it is fully charged is approximately 6.9 volts.
The components enclosed within box 124 in FIG. 2 perform the
function of Current Control Loop 124 in FIG. 1. These components
control SCRs 220 and 224 by applying a proper voltage and current
at the anodes 228A and 230A of diodes 228 and 230, respectively.
Diodes 228 and 230 are connected to gates 220C and 224C of SCRs 220
and 224, respectively, so that SCRs 220 and 224 will be "gated on"
for the proper period of time to maintain a constant or otherwise
desired charge current through battery 234. The period of time when
SCRs 220 and 224 are gated on will be referred to as their "duty
cycle."
In accordance with one aspect of the present invention, sensing
means are provided for producing a sensed voltage proportional to
the current through a load, such as battery 234. By way of example,
resistor 232 is placed in the charge current path to produce a
sensed voltage which is directly proportional to the instantaneous
charge current.
In accordance with the present invention, there is also provided
integration means for integrating the sensed voltage produced by a
sensing element, such as resistor 232, and for producing therefrom
an integrated signal representing the average current flow through
a load, such as battery 234. As shown in FIG. 2 by way of example
and not limitation, the second terminal 234B of resistor 232 is
connected through a resistor 236 to the inverting input 240 of
amplifier 244. Amplifier 244 may be one of many commercially
available operational amplifiers, which are fabricated as
integrated circuits. It is preferred that amplifier 244 be of the
type generally designated in the art as TLC271; however, other
types of amplifiers, including those using discrete components,
could also be used.
A resistor 238 is connected between inverting input 240 and output
246 of amplifier 244. Noninverting input 242 of amplifier 244 is
tied to circuit common 300, thus causing amplifier 244 to operate
as an inverting amplifier. Resistor 236 preferably has a value of
10 Kohms, while resistor 238 preferably has a value of 27 Kohms.
Amplifier 244 thus has a gain of approximately 2.7.
Included in the invention is an averaging means for averaging a
sensed voltage, such as appears across resistor 232, and has been
processed by an input amplifier, such as amplifier 244, to produce
an averaged sensed voltage. As illustrated in the embodiment of the
present invention shown in FIG. 2, output 246 of amplifier 244 is
connected to one side of a resistor 248, which preferably has a
value of about 100 Kohms. A capacitor 250 preferably having a value
of approximately 2.2 microfarads and rated at at least 20 volts is
connected between the other side of resistor 248 and circuit common
300 at a junction 252.
The function of capacitor 250 and resistor 248 is to integrate or
average the output of amplifier 244. Thus, pulses which are applied
to input 240 of amplifier 244 are amplified and then integrated by
the RC circuit formed by resistor 248 and capacitor 250 connected
to output 246 of amplifier 244. The values for capacitor 250 and
resistor 248 are chosen so that the RC circuit has a time constant
that produces a DC voltage output at junction 252 that is
proportional to the average charge current.
In accordance with yet another aspect of the present invention,
there is also provided comparison means for comparing the
integrated signal representing the average current flow through a
load, such as battery 234, and producing a corresponding control
signal. By way of example, as shown in FIG. 2, the DC voltage at
junction 252 is supplied to a first comparator 254 at the inverting
input 256 thereof. First comparator 254, as well as second
comparator 264 and third comparator 288, which will be described
shortly, may be of the type commonly designated in the art as TLC
374. Nevertheless many different types of comparators, or even
other types of components, may perform the same function and
fulfill the purpose of the components specified.
A reference voltage generator represented by block 274 is utilized
in relation to first, second, and third comparators 254, 264 and
288, respectively. It will be appreciated that many different
devices are available in the art which generate an accurate
reference voltage. The reference voltage generator 274 may
preferably be a device generally designated in the art as MC
1403.
Resistors 270 and 272 connected in series between reference voltage
generator 274 and circuit common 300 form a voltage divider which
"divides down" the reference voltage provided by reference voltage
generator 274. The "divided down" reference voltage appearing
across resistor 272 is applied to noninverting input 258 of first
comparator 254. Thus, the signal at output 260 of first comparator
254 will change states when the voltage applied to inverting input
256 thereof ceases to be equal to the "divided down" reference
voltage applied to noninverting input 258. In this way, the signal
at output 260 of first comparator 254 can be made to reflect
whether the charge current through battery 234, as represented by
the DC voltage at junction 252, is at the proper level.
The signal at output 260 of first comparator 254 is conducted to
inverting input 266 of second comparator 264. The noninverting
input 268 of second comparator 264 is tied to the undivided output
voltage of voltage reference generator 274. Thus, second comparator
264 merely inverts the signal applied to it at its inverting input
266.
In another aspect of the circuit of the present invention, means
are provided for isolating the output of a comparator, such as
second comparator 264, from a switching device, such as that
included in block 106, which is to be controlled by the output of
the comparator. As shown in circuit 200 of FIG. 2, by way of
example, the signal at output 262 of second comparator 264 is
connected to an opto-isolator 278 through a resistor 276, which may
have a value of 330 ohms. Opto-isolator 278 may be of the type
generally s 2 designated in the art as 4N37. The internal
components of opto-isolator 278 consist of a light emitting diode
280 (LED), having a cathode 280B connected to resistor 276 and an
anode 280A connected to transformer secondary center tap 216.
Opto-isolator 278 also includes a phototransistor generally
designated 282. Collector 282A of phototransistor 282 also
connected to transformer secondary center tap 216, while
phototransistor base 282C is optically coupled to LED 280. The
output of opto-isolator 278 appearing at the emitter 282B of
phototransistor 282 is connected to anodes 228A and 230A of diodes
228 and 230, respectively, in box 106. By the above-described
arrangement, it can be clearly seen that a current control loop is
formed from the components shown in box 124 and described
above.
As mentioned earlier, it is undesirable to overcharge a battery.
One indication that a battery is being overcharged is a high
terminal voltage. For example, as mentioned earlier, a battery
designed for use with the embodiment illustrated in FIG. 2 may have
achieved its maximum charge once its terminal voltage has reached
6.9 volts. Thus, by monitoring the terminal voltage of battery 234,
overcharging can be avoided.
Accordingly, in yet another aspect of the present invention,
overvoltage protection means are provided for preventing a current
control loop, such as that represented by the elements shown in box
124 of FIG. 2, from increasing the duty cycle of a switching
device, such as that shown within box 106 of FIG. 2, if the voltage
across the terminals of a recharging battery is greater than or
equal to a predetermined threshold voltage value. Such a function
is carried out by the components contained within box 118, which
will collectively and alternatively be referred to as an
overvoltage protection circuit.
One aspect of the overvoltage protection means include a means for
comparing the voltage across the terminals of a battery to some
reference voltage, thereby to detect when the voltage across such
battery terminals exceeds a predetermined threshold voltage level.
As shown in FIG. 2, resistors 284 and 286 in combination with third
comparator 288 exemplify one manner in which this function can be
performed. Resistors 284 and 286 are series connected such that one
side of resistor 284 is connected to transformer secondary center
tap 216 and first terminal 234A of battery 234 and the other side
is connected to one side of resistor 286. The other side of
resistor 284 is connected to circuit common 300. Thus, resistors
284 and 286 form a voltage divider that is connected in parallel
with battery 234.
In the embodiment illustrated in FIG. 2, resistors 284 and 286 have
a value of 10 Kohms and 1 Mohms, respectively. A divided battery
terminal voltage appears across resistor 284 and is applied to
noninverting input 290 of third comparator 288. Inverting input 292
of third comparator 288 receives the undivided reference voltage
from reference voltage generator 274. When the values of resistors
284 and 286 have properly selected, the signal at output 294 of
third comparator 288 will become positive when the terminal voltage
of battery 234 as divided by resistors 284 and 286 and applied to
noninverting input 290 of third comparator 288 exceeds a
predetermined threshold voltage corresponding to the voltage
produced by reference voltage generator 274 as applied to inverting
input 292 of third comparator 288.
In another aspect of the overvoltage protection means, means are
provided for reducing the charge current through a battery, such as
battery 234, when the voltage across the battery terminals reaches
a predetermined threshold voltage. In the embodiment of the
invention illustrated in FIG. 2, this involves interrupting the
control of the charge current normally exercized by a current
control loop, such as that exemplified by the devices contained
within block 124 of FIG. 2. Thus, a positive signal at output 294
of third comparator 288 is conducted through a diode 296 and a
resistor 298 to junction 252 in box 124. Diode 296 may be identical
to any of the diodes described earlier, and resistor 298 may have a
value of 470 Kohms.
With the voltage output of third comparator 288 thus applied to
junction 252, when the terminal voltage of battery 234 exceeds a
preselected threshold voltage, overvoltage protection circuit 118
will cause the voltage at point 252 to increase. This interrupts
the normal operation of the current control loop within box 124,
causing the duty cycle of SCRs 220 and 224 to be reduced, or even
causing SCRs 220 and 224 to be gated off. Battery 234 is thus
protected from being overcharged.
The components contained within box 130 function as a DC power
source, for the active components of circuit 200. In the
illustrated embodiment of FIG. 2, an auxiliary transformer
secondary winding 302 on laminated core 210 has two terminals 304
and 306 which are connected to a bridge rectifier 308. The positive
DC output of bridge rectifier 308 is filtered with a capacitor 310
and then is distributed to the various active components of circuit
200, as indicated by arrow 312. It will be appreciated that many
different circuit configurations would serve the function performed
by the components within box 130.
Having an understanding of the general configuration of the
structure of the presently preferred embodiment, the operation of
embodiment will now be explained next.
3. Operation of the Presently Preferred Embodiment
As explained earlier, alternating current is applied to the primary
winding 208 of the transformer. A closed s current path is formed
by transformer secondary center tap 216, battery 234, resistor 232,
SCRs 220 and 224, and first transformer secondary 212. By the use
of a center tapped transformer and two SCRs, full wave
rectification of the AC waveform is effected.
It will be appreciated that in the embodiment illustrated in FIG.
2, current flow through battery 234 will occur only when SCRs 220
and 224 are gated on. Thus, since full wave rectification occurs,
either SCR 220 or SCR 24 will conduct on alternate half cycles of
the AC waveform. The use of SCRs 220 and 224 as both rectifiers and
switching devices provides for considerable savings in components,
increased efficiency, and decreased heat generation.
In operation, the charge current flows through resistor 232
generating a sensed voltage at the junction of resistor 232 and
SCRs 220 and 224. The sensed voltage is a series of negative pulses
having a sinusoidal shape, or a partial sinusoidal shape when SCRs
220 and 224 are gated "on" at midcycle. The negative voltage pulses
are amplified and inverted by amplifier 224.
The output of amplifier 224 is integrated, or averaged, by the RC
circuit formed by resistor 248 and capacitor 250. The DC voltage
present at junction 252 is directly proportional to the average
sensed current through sensing resistor 232 and battery 234. The
average voltage present at junction 252 is compared by first
comparator 254 against a divided reference voltage, provided by
reference voltage generator 274 and the voltage divider formed by
resistors 270 and 272. The output of first comparator 254 is
inverted by second comparator 264, and the output of second
comparator 264 is used to drive opto-isolator 278. The output of
opto-isolator 278 sources the gate current for SCRs 220 and 224,
thus completing a current control loop which controls the average
charge current at a constant level.
As battery 232 is charged, the battery terminal voltage rises. The
battery terminal voltage is continuously monitored by a third
comparator 288 through a resistive divider circuit formed by
resistors 284 and 286. The values of resistors 284 and 286 are
chosen such that when the battery terminal voltage reaches its full
charge level, the voltage present at the divider will equal the
reference voltage supplied by reference voltage generator 274,
causing the output signal of third comparator 288 to change to a
positive state.
Once this occurs, comparator 288 will source current through diode
296 and resistor 298 to junction 252. The voltage at junction 252
will rise, the current control loop within box 124 will be
interrupted, and the SCRs 220 and 224 will tend to be gated off,
reducing their duty cycle. This condition will continue until the
voltage across the terminals of battery 234 returns below that
level which causes third comparator 288 to go positive. At that
time the output of comparator 288 will become negative and the
current control loop within box 124 will resume normal
operation.
4. Description of the Detailed Schematic of the Preferred
Embodiment
As explained earlier, the embodiment of the circuit 200 shown in
FIG. 2 has been simplified in order to increase the clarity of the
disclosure and to facilitate an understanding of its operation.
Therefore, some components and interconnections have not been
shown. FIG. 3 presents a detailed schematic diagram of a presently
preferred embodiment of circuit 200 illustrated in FIG. 2. As in
FIG. 2, the charge current paths in FIG. 3 have been indicated by
bold lines. The "pin outs" of the components have been shown in
FIG. 3 where appropriate.
Provided below is a table listing the values of the components
referenced in the detailed schematic of FIG. 3.
______________________________________ Component Designation
Description ______________________________________ Z1 Opto-Isolator
4N37 Z2 Operational Amplifier TLC271 Z3 Voltage Reference MC1403 Z4
Quad Comparator TLC374 Q1-Q2 SCR S4060F CR2-CR5 Diode 1N4001
CR6-CR8 Diode 1N4148 R2-R4 Resistor .1 ohm 2 watts R5-R6 Resistor 1
Kilohm 1/4 watt 5% R7 Resistor 10 Kilohm 1/4 watt 5% R8 Resistor 15
Kilohm RN55C R9 Resistor 8.06 Kilohm RN55C R10 Resistor 27 Kilohm
1/4 watt 5% R11 Resistor 100 Kilohm 1/4 watt 5% R12 Resistor 47.0
Kilohm 1/4 watt 5% R13 Resistor 10 Kilohm 1/4 watt 5% R15 Resistor
330 Ohm 1/4 watt 5% R16 Resistor 220 ohm 1/4 watt 5% R17 Resistor
5.1 Kilohm 1/4 watt 5% R18 Resistor 1 megohm 1/4 watt 5% R19
Resistor 2.4 Kilohm 1/4 watt 5% R23 Resistor 10 Kilohm 1/4 watt 5%
R24 Resistor 1 megohm 1/4 watt 5% R25 Resistor 10 Kilohm 1/4 watt
5% R35 Resistor 10 Kilohm 1/4 watt 5% C1 Capacitor 68 microfarad 20
volt C2 Capacitor 2.2 microfarad 20 volt C5 Capacitor 0.1
microfarad 50 volts C6 2.2 microfarad 20 volts T1 Transformer 120
volt primary 16 volt center tapped 8 volt secondary B1 "Gel-Cell"
battery 6 volt, 10 amp hours F1 Fuse 3 amp slow-blow type F2 Fuse
.5 amp slow-blow type ______________________________________
SUMMARY
As will be appreciated from the foregoing description, the present
invention provides an efficient regulated battery charger which
maintains high efficiency even over a wide range of voltages. Still
further, due to the small number of components necessary to
implement the present invention, embodiments of the present
invention may be housed in a physically small space. Because of the
relatively high efficiency of the present invention, little heat is
generated, thus facilitating the enclosure of embodiments
incorporating the present invention in compact housings with little
or no ventilation.
All of the above listed advantages are gained while still avoiding
the problem of producing radio frequency interference common in
other type of high efficiency switching-type regulators. The
present invention is also provided with means for monitoring the
terminal voltage of a rechargeable battery and preventing its
overcharging. Importantly, the present invention maintains a
constant average charge current through the battery, thus allowing
the recharging process to be predictably carried on.
The present invention may be embodied in other specific forms
without departing from its spirit or essential characteristics. The
described embodiment is to be considered in all respects only as
illustrative and not restrictive. The scope of the invention is,
therefore, indicated by the appended claims rather than by the
foregoing description. All changes which come within the meaning
and range of equivalency of the claims are to be embraced within
their scope.
* * * * *